Interpretive Summary:
Making fine wine begins in the vineyard with the production of high quality fruit. Viruses, such as Grapevine leafroll associated viruses (GLRaVs) can have negative impacts on both vine productivity and fruit quality. Recent reports on the incidence and spread of GLRaVs in vineyards in Oregon and Washington led to this study on the impact of these viruses on phenolic compounds in 'Pinot noir', the dominant and most valuable wine grape cultivar grown in Oregon. This paper reports on the impact of GLRaV-2 or -3 positive samples compared to healthy vines (GLRaV tested negative) from commercially operating vineyards. Overall, GLRaV infected vines had lower pigment content and percent soluble solids. There were differences in virus response in the other biochemical components found in the berries.

Technical Abstract:
Some of the ten known Grapevine leafroll associated viruses (GLRaVs) have negative impacts upon vine productivity and grape quality, though these negative influences are dependent on factors such as GLRaV, cultivar, clone, rootstock, and vine age. This is the first study to report on GLRaV-2 and GLRaV-3 infected vines with regard to phenolic compounds, and other fruit maturity indices, found in 'Pinot noir' grapes, compared to berries from adjacent vines free of GLRaVs (same vineyards). Three different rootstock / scion combinations were included in this study. Clusters were collected for two growing seasons from commercial vineyards in the Willamette Valley of Oregon, and each vine sampled was tested for GLRaV-1, -2, -3 and Rupestris stem pitting-associated virus (RSPaV). All sampled vines were infected with RSPaV. Grapevine leafroll associated virus infected vines tested positive for GLRaV-2 or GLRaV-3. Overall, GLRaV-2 and -3 infected fruit had reduced percent soluble solids, decreased individual and total anthocyanins, and increased skin and pulp weight for all three ‘Pinot noir’ rootstock / scion combinations examined. Vitis riparia rootstock / 'Pinot noir' clone 114 scion combination appeared to be the most sensitive to GLRaV-3 infection, having significant reduction of all five anthocyanins, total phenolics, total tannins, with an increased cluster weight and 100 berry weight. No clear trends were observed in the polyphenolics analyzed.